My thermometer is very accurate. Same in my Mercury. Just have to remember what it is measuring. If you are moving forward, you are measure the air temp about 3 feet above the pavement. If it is a windy cold/cool day, it should be accurate. If not, get it replaced. If it is a very hot no wind day, then the convection heat from the pavement will add a few degrees. At 80 degrees, it may add 1. At 85, 2. At 90, 3. Etc. The Av is less susceptible since the probe is higher than on a car. On my car I actually created a calibration chart to determine the "real" temp when it got over 80 degrees. And if you are sitting still, all bets are off since the engine heat is leaking forward.
I also had another vehicle where the probe could see the sun. Once i shaded it, it was accurate again.